System for irradiating charged particles and method for irradiating charged particles

ABSTRACT

A charged particle irradiation system is capable of shortening the irradiation time and the treatment time by performing efficient irradiation even when irregular variation occurs in the irradiation object during the gating irradiation. The extraction of the beam is stopped upon reception of a regular extraction permission end signal which is outputted based on a regular movement signal. An extractable state maintaining function operates upon the reception of the extraction permission end signal. When a preset standby time elapses without receiving an extraction permission start signal again during the standby time, the extractable state maintaining function finishes its operation and a charged particle beam generator decelerates the beam. Also, the extraction of the beam is stopped due to reception of an irregular extraction permission end signal during the irradiation. When the extraction permission start signal is received again during the standby time, the extraction of the beam is restarted.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of Ser. No. 14/361,416,filed May 29, 2014, the entire disclosure of which is incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a charged particle irradiation systemand a charged particle irradiation method, and in particular, to acharged particle irradiation system and a charged particle irradiationmethod for treating a target volume (e.g., tumor) by irradiating thetarget volume with a charged particle beam.

BACKGROUND ART

There is a well-known method of treating cancer patients, etc. byirradiating a target volume in the patient's body with a chargedparticle beam (ion beam) such as a proton beam. The system used for theirradiation comprises a charged particle beam generator, a beamtransport line, and a treatment room.

The charged particle beam accelerated by the charged particle beamgenerator reaches an irradiation nozzle (irradiation device) in thetreatment room via the beam transport line. The distribution of thecharged particle beam is broadened by the irradiation nozzle and anirradiation field suitable for the shape of the target volume is formedin the patient's body. The irradiation nozzle may also be equipped witha scanning device which performs the scanning of the charged particlebeam in conformity to the shape of the target volume.

Incidentally, since precise irradiation becomes difficult when thetarget (e.g. target volume) moves due to the patient's respiration orthe like, the gating irradiation (irradiating the target only when thetarget is at a preset position (in an extraction permission area)) iscarried out.

In a conventional technology described in Patent Literature 1, thegating irradiation is performed by using a synchrotron as a chargedparticle beam generator that repeats theinjection/acceleration/extraction/deceleration of the beam. The periodiccycle time of the injection/acceleration/extraction of the beam iscontrolled in order to effectively use the beam in the gatingirradiation.

PRIOR ART LITERATURE Patent Literature

Patent Literature 1: JP-2921433-B

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In the gating irradiation, the irradiation is performed in sync with thecycle of the patient's respiration or the like. Although the respirationcycle is generally regular to some extent, the respiration cycle canchange irregularly since the respiration is based on the physiologicalactivity of the patient.

In the conventional technology, the charged particle beam generatorstarts the deceleration immediately when the target deviates from theextraction permission area. Thus, in cases where the target returns tothe extraction permission area after deviating from the extractionpermission area for a short time (irregular variation), the chargedparticle beam generator has already started the deceleration and thebeam extraction cannot be performed even though the target is within theextraction permission area. Since efficient irradiation is impossible asabove, the total irradiation time tends to be long, and consequently,the treatment time is liable to be long in the conventional technology.

It is therefore the primary object of the present invention to provide acharged particle irradiation system and a charged particle irradiationmethod capable of shortening the irradiation time and the treatment timeby performing efficient irradiation even when irregular variation occursin the irradiation object during the gating irradiation.

Means for Solving the Problem

(1) To achieve the above object, the present invention provides acharged particle irradiation system comprising: a charged particle beamgenerator that repeats injection of charged particles, acceleration ofthe charged particles, an extractable state after finishing theacceleration, and deceleration of the charged particles; an irradiationnozzle that irradiates an irradiation object with a charged particlebeam supplied from the charged particle beam generator; and a controlsystem that controls the charged particle beam generator and theirradiation nozzle, the control system having: an irradiation objectstate variation signal reception function of receiving signals from anirradiation object monitoring device that monitors state variation ofthe irradiation object; an extraction permission state setting functionof setting an extraction permission state by outputting an extractionpermission signal in sync with the state variation of the irradiationobject; and an extraction control function of commanding chargedparticle beam extraction when the charged particle beam generator is inthe extractable state and in the extraction permission state, whilecommanding stoppage of the charged particle beam extraction when thecharged particle beam generator is not in the extraction permissionstate even if the charged particle beam generator is in the extractablestate. The control system further has an extractable state maintainingfunction that operates after the end of the extraction permission stateand maintains the extractable state of the charged particle beamgenerator even after the end of the extraction permission state. Theextraction control function commands the charged particle beamextraction again when the extraction permission state starts againduring the operation of the extractable state maintaining function,while commanding the deceleration of the charged particle beam generatorafter the end of the operation of the extractable state maintainingfunction.

In the conventional technology, when the extraction permission stateends, the extraction control function commands the stoppage of theextraction and immediately commands the deceleration of the chargedparticle beam generator. Even in cases where the target returns to theextraction permission state in a short time (irregular variation), thecharged particle beam generator has already started the deceleration andthe beam extraction cannot be performed even though it is in theextraction permission state. Since efficient irradiation is impossibleas above, the total irradiation time tends to be long, and consequently,the treatment time is liable to be long in the conventional technology.

In contrast, owing to the operation of the above-described extractablestate maintaining function, the extraction control function does notimmediately command the deceleration of the charged particle beamgenerator even when commanding the stoppage of the extraction after theend of the extraction permission state. When the extraction permissionstate starts again during the operation of the extractable statemaintaining function, the extraction control function commands thecharged particle beam extraction again.

With this configuration, it is possible to perform efficient irradiationand shorten the irradiation time and the treatment time.

(2) Preferably, in the above charged particle irradiation system (1),the extractable state maintaining function operates for a preset standbytime.

With this configuration, the extractable state of the charged particlebeam generator is maintained for the preset standby time. When theextraction permission state starts again before the elapse of the presetstandby time, the extraction control function commands the chargedparticle beam extraction again.

(3) Preferably, in the above charged particle irradiation system (2),the extractable state maintaining function starts operating based on asignal that commands termination of the extraction permission state.

(4) Preferably, in the above charged particle irradiation system (2),the extractable state maintaining function starts operating based on asignal that commands the stoppage of the charged particle beamextraction.

The above configurations (3) and (4) set the starting point of thepreset standby time.

(5) Preferably, in the above charged particle irradiation system (1),the extractable state maintaining function operates only while the statevariation of the irradiation object is within a preset range.

With this configuration, the extractable state of the charged particlebeam generator is maintained only while the state variation of theirradiation object is within the preset range. When the extractionpermission state starts again while the state variation of theirradiation object is within the preset range, the extraction controlfunction commands the charged particle beam extraction again.

(6) Preferably, in the above charged particle irradiation system (1),the extraction control function commands the stoppage of the chargedparticle beam extraction after reception of a signal commandingtermination of the extraction permission state and after irradiationwith a prescribed dose.

With this configuration, in cases of spot irradiation, interruption ofthe irradiation during the spot irradiation can be eliminated andsimpler control can be achieved.

(7) To achieve the above object, the present invention provides acharged particle irradiation method for a charged particle irradiationsystem equipped with a charged particle beam generator, an irradiationnozzle and a control system that controls the charged particle beamgenerator, the irradiation nozzle and an irradiation object monitoringdevice, comprising: an extraction standby step in which the chargedparticle beam generator repeats injection of charged particles,acceleration of the charged particles, an extractable state afterfinishing the acceleration, and deceleration of the charged particles;an irradiation object state variation monitoring step in which theirradiation object monitoring device monitors state variation of anirradiation object; an extraction permission state setting step ofsetting an extraction permission state in sync with the state variationof the irradiation object monitored in the irradiation object statevariation monitoring step; an extraction step of extracting a chargedparticle beam from the charged particle beam generator and having theirradiation nozzle apply the charged particle beam to the irradiationobject when the charged particle beam generator is in the extractablestate in the extraction standby step and in the extraction permissionstate due to the extraction permission state setting step; and anextraction stoppage step of stopping the extraction when the chargedparticle beam generator is not in the extraction permission state due tothe extraction permission state setting step even if the chargedparticle beam generator is in the extractable state in the extractionstandby step. The charged particle irradiation method further comprisesan extractable state maintaining step of maintaining the extractablestate of the charged particle beam generator even after the extractionpermission state ends in the extraction permission state setting step.In the extraction step, the charged particle beam is extracted againwhen the extraction permission state starts again in the extractionpermission state setting step during the maintenance of the extractablestate by the extractable state maintaining step. In the extractionstandby step, the charged particle beam generator decelerates the beamafter the end of the maintenance of the extractable state by theextractable state maintaining step.

Effect of the Invention

According to the present invention, the irradiation time and thetreatment time can be shortened by performing efficient irradiation evenwhen irregular variation occurs in the irradiation object during thegating irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing the overall configuration ofa charged particle irradiation system (first embodiment).

FIG. 2 is a schematic diagram showing the configuration of anirradiation nozzle.

FIG. 3A is a graph for explaining the relationship between the depth ofthe target and the energy of the ion beam.

FIG. 3B is a graph for explaining the relationship between the depth ofthe target and the energy of the ion beam.

FIG. 4 is a graph for explaining the relationship between the ion beamand the lateral dimension of the irradiation target in a directionorthogonal to the beam axis (direction parallel to an XY plane).

FIG. 5 shows data structure of irradiation parameters registered in adatabase.

FIG. 6 is a control flow chart showing the details of processing by anirradiation object monitoring controller and a central controller.

FIG. 7 is a control flow chart showing the details of processing by anirradiation controller.

FIG. 8 is a conceptual diagram for explaining the operation of thecharged particle irradiation system.

FIG. 9 is a control flow chart showing the details of processing by thecentral controller (conventional technology).

FIG. 10 is a conceptual diagram for explaining the operation of thecharged particle irradiation system (conventional technology).

FIG. 11 is a control flow chart showing the details of processing by thecentral controller (second embodiment).

FIG. 12 is a conceptual diagram for explaining the operation of thecharged particle irradiation system (second embodiment).

FIG. 13 is a control flow chart showing the details of processing by theirradiation controller (third embodiment).

MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, a description will be given in detail ofpreferred embodiments of the present invention.

First Embodiment

Configuration

FIG. 1 is a schematic block diagram showing the overall configuration ofa charged particle irradiation system. The charged particle irradiationsystem comprises a charged particle beam generator 1, a beam transportline 2, a radiation treatment room 17, a control system 7, anirradiation object monitoring controller 65, and an irradiation objectmonitoring device 66. Further, an X-ray CT 40 and an irradiationplanning device 41 are arranged as equipment related to the chargedparticle irradiation system.

The charged particle beam generator 1 includes an ion source (unshown),a linear accelerator 3 (charged particle beam preaccelerator) and asynchrotron 4. The synchrotron 4 includes a radiofrequency waveapplication device 5 and an accelerator 6. The radiofrequency waveapplication device 5 includes a radiofrequency power supply 9 andradiofrequency electrodes 8 arranged in the closed orbit of thesynchrotron 4. The radiofrequency power supply 9 is connected to theradiofrequency electrodes 8 via a switch (unshown). The accelerator 6includes a radiofrequency acceleration cavity (unshown) arranged in theclosed orbit of the ion beam and a radiofrequency power supply (unshown)for applying radiofrequency electric power to the radiofrequencyacceleration cavity. An extraction deflector 11 connects the synchrotron4 to the beam transport line 2.

The beam transport line 2 includes a beam path 12, quadrupole magnets(unshown), and bending magnets 14, 15 and 16. The beam path 12 isconnected to an irradiation nozzle (irradiation device) 21 which isarranged in the treatment room 17.

A rotating gantry (unshown) is installed in the treatment room 17. Theirradiation nozzle 21 and the bending magnets 15 and 16 as parts of thebeam transport line 2 are arranged in the rotating gantry. A treatmentbed (referred to as a “couch 24”) and the irradiation object monitoringdevice 66 for measuring the movement of the irradiation object 25 on thebed are arranged inside the rotating gantry.

The rotating gantry is configured to be rotatable by a motor. Thebending magnets 15 and 16 and the irradiation nozzle 21 rotate alongwith the rotation of the gantry. Owing to the rotation, the irradiationobject 25 can be irradiated from any direction in a plane orthogonal tothe rotation axis of the gantry.

FIG. 2 is a schematic diagram showing the configuration of theirradiation nozzle 21. The irradiation nozzle 21 includes a scanningmagnet 31, a scanning magnet 32, a beam position monitor 33, and a dosemonitor 34. In the charged particle irradiation system of thisembodiment, the irradiation nozzle 21 is equipped with two scanningmagnets 31 and 32 and the irradiation position is changed by deflectingthe ion beam in two directions (X direction, Y direction) in a planeorthogonal to the beam propagation direction. The beam position monitor33 measures the position and the broadening of the ion beam. The dosemonitor 34 measures the amount of the irradiating ion beam. Anirradiation target 37 exists in the irradiation object 25. By theirradiation with the ion beam, a dose distribution covering theirradiation target 37 is formed inside the irradiation object 25. In thetreatment of cancer or the like, the irradiation object 25 is a human(patient) and the irradiation target 37 is a tumor (target volume).

FIGS. 3A and 3B are graphs for explaining the relationship between thedepth of the target and the energy of the ion beam. FIG. 3A indicates adose distribution formed in the irradiation object by a single-energyion beam as a function of the depth, while FIG. 3B indicates a dosedistribution formed in the irradiation object by several ion beams ofdifferent energy levels as a function of the depth. The peak shown inFIG. 3A is called a “Bragg peak”. Since the position of the Bragg peakchanges depending on the energy, irradiation of the irradiation targetat the Bragg peak position is possible by adjusting the energy of theion beam to suit the depth of the irradiation target. The irradiationtarget has a certain thickness in the depth direction, whereas the Braggpeak is a sharp peak. Therefore, a uniform high-dose region (SOBP(spread-out Bragg peak)) having the same thickness in the depthdirection as the irradiation target is formed by superimposing severalBragg peaks as shown in FIG. 3B, by performing the irradiation by use ofseveral ion beams of different energy levels in an appropriate intensityratio.

FIG. 4 is a graph for explaining the relationship between the ion beamand the lateral dimension of the irradiation target in a directionorthogonal to the beam axis (direction parallel to the XY plane). Eachdirection orthogonal to the beam axis will hereinafter be referred to asa “lateral direction”. After entering the irradiation nozzle 21, the ionbeam is scanned (deflected) by the two scanning magnets 31 and 32arranged orthogonal to each other and reaches an intended position inthe lateral direction. The broadening of the ion beam in the lateraldirection can be approximated by the shape of a Gaussian distribution.If a plurality of identical Gaussian distributions are arranged at evenintervals while setting the interval substantially at the standarddeviation of the Gaussian distribution, the distribution formed by thesuperimposed (overlapped) Gaussian distributions has a uniform region.Each of the Gaussian distribution-like dose distributions arranged asabove is referred to as “spot”. A dose distribution that is uniform inthe lateral direction can be formed by arranging a plurality of spots ateven intervals by scanning the ion beam.

As explained above, a uniform irradiation field can be formed by thebeam scan in the lateral direction by using the scanning magnets and theBragg peak shift in the depth direction by changing the beam energy.Incidentally, a unit of the irradiation field, irradiated with the sameenergy and having a certain broadening in the lateral direction due tothe ion beam scan by the scanning magnets, is referred to as a “slice”.

Returning to FIG. 1, the irradiation planning device 41 and anaccompanying configuration will be explained below.

Before the irradiation of the irradiation target 37 with the ion beam iscarried out, the irradiation planning device 41 determines parametersnecessary for the irradiation. The parameters are determined asexplained below.

The irradiation object 25 is previously image-captured by the X-ray CTdevice 40. Further, a patient movement signal outputted from an unshowndevice (equivalent to the irradiation object monitoring device 66)attached to the X-ray CT device 40 is acquired. The X-ray CT device 40generates image data of the irradiation object 25 based on the acquiredimaging data and sends the generated image data to the irradiationplanning device 41. The irradiation planning device 41 displays thereceived image data on the screen of a display device (unshown). When aregion that should be irradiated is specified on the image by theoperator, the irradiation planning device 41 generates data necessaryfor the irradiation, calculates a dose distribution that is expected inthe irradiation by use of the data, and displays the calculated dosedistribution on the display device. The region that should be irradiatedis specified so as to cover the irradiation target 37. The irradiationplanning device 41 calculates and determines an irradiation objectsetting position (position where the irradiation object 25 should beset), a gantry angle, and irradiation parameters with which the dosedistribution can be formed in the specified region. Further, theirradiation planning device 41 determines the initial position of thecouch 24 and also determines the extraction permission area based on theacquired movement signal.

The irradiation parameters include the energy of the ion beam,positional information (X coordinate, Y coordinate) in a planeorthogonal to the beam axis, and a target irradiation amount of the ionbeam for the irradiation of each position. Specifically, the irradiationplanning device 41 divides the irradiation target (target volume) 37into a plurality of slices arranged in the depth direction based onpatient information inputted by the operator and determines the number Nof necessary slices (slice count N). The irradiation planning device 41also determines the ion beam energy Ei suitable for the irradiation ofeach slice (slice No. i) according to the depth of each slice. Further,according to the shape of each slice, the irradiation planning device 41determines the number Ni of irradiation spots to be irradiated with theion beam (spot count Ni), spot numbers j, the irradiation position (Xij,Yij) of each spot, and the target irradiation amount Dij for each spot.

The irradiation planning device 41 sends the information (data)determined as above to a database 42. The database 42 records the dataoutputted from the irradiation planning device 41.

FIG. 5 shows the data structure of the irradiation parameters registeredin the database 42. The irradiation parameters include the slice count Nand data regarding each slice. The data regarding each slice includesthe slice number i, the energy Ei, the spot count Ni, and data regardingeach spot. The data regarding each spot includes the spot number j, theirradiation position (Xij, Yij), and the target irradiation amount Dij.

Returning to FIG. 1, a configuration related to the control system ofthe charged particle irradiation system will be explained below.

The irradiation object monitoring device 66 is an instrument capable ofmeasuring the movement of the target 37 or an amount that changes inconjunction with the movement. For example, the irradiation objectmonitoring device 66 may be implemented by a laser distance meter formeasuring the movement of the body surface of the patient, anaeroplethysmograph for measuring the amount of the patient's exhalation,a device for measuring the pressure in a belt wound around the patient'sabdomen, etc. In order to use these methods, it is necessary topreviously (before the treatment) determine the relationship between theoutput of the measuring instrument and the position of the target. Theirradiation object monitoring device 66 may also be implemented by adevice that determines the position of a marker inserted in the vicinityof the target 37 (or the position of the target 37 itself) by means ofroentgenography. Incidentally, the irradiation object monitoring device66 may be provided either as a component of the charged particleirradiation system or as an external instrument added to the chargedparticle irradiation system.

The irradiation object monitoring device 66 is controlled by theirradiation object monitoring controller 65. The irradiation objectmonitoring controller 65 receives a movement signal from the irradiationobject monitoring device 66 and outputs an extraction permission signalbased on comparison between the movement signal and the extractionpermission area. The extraction permission area, which has been setpreviously, is sent from the irradiation planning device 41. Theextraction permission area may also be designated by the operator. Theextraction permission signal includes an extraction permission startsignal and an extraction permission end signal. The state (period)between the outputting of the extraction permission start signal and theoutputting of the extraction permission end signal by the irradiationobject monitoring controller 65 is set as an extraction permissionstate. The irradiation object monitoring controller 65 may also beprovided as a component of the control system 7.

The control system 7 includes the database (data storage device) 42, acentral controller 46, an accelerator controller 47, and an irradiationcontroller 48. The database 42 is connected to the irradiation planningdevice 41. The data necessary for the irradiation generated by theirradiation planning device 41 are stored in the database 42.

The central controller 46 is connected to the accelerator controller 47,the irradiation controller 48 and the database 42. The centralcontroller 46 receives data from the database 42, sends necessaryinformation to the accelerator controller 47 and the irradiationcontroller 48, and thereby controls the controllers 47 and 48.

The accelerator controller 47 is connected to the charged particle beamgenerator 1, the beam transport line 2 and the rotating gantry tocontrol them. For example, the accelerator controller 47 performs thecontrol so that the charged particle beam generator 1 repeats theinjection of the charged particles, the acceleration of the chargedparticles, an extractable state after finishing the acceleration, andthe deceleration of the charged particles and so that the chargedparticle beam generator 1 extracts (emits) the charged particle beamwhen the charged particle beam generator 1 is in the extractable state.The irradiation controller 48 controls the amounts of excitationcurrents flowing through the scanning magnets 31 and 32 while alsoprocessing the monitoring signals inside the irradiation nozzle 21.

The central controller 46 has various computation functions. A gatingirradiation function 46 a is one of the computation functions of thecentral controller 46. The gating irradiation function 46 a commands thecharged particle beam extraction when the charged particle beamgenerator 1 is in the extractable state and in the extraction permissionstate. The gating irradiation function 46 a commands stoppage of thecharged particle beam extraction when the charged particle beamgenerator 1 is not in the extraction permission state even if thecharged particle beam generator 1 is in the extractable state.

The central controller 46 has an extractable state maintaining function46 b as a characteristic function of this embodiment. The extractablestate maintaining function 46 b waits on standby for a preset standbytime when the extraction permission end signal is received from theirradiation object monitoring controller 65. Consequently, theextractable state of the charged particle beam generator 1 is maintainedfor the preset standby time.

The gating irradiation function 46 a commands the charged particle beamextraction again when the extraction permission start signal is receivedagain from the irradiation object monitoring controller 65 during thepreset standby time. If the extraction permission start signal is notreceived again, after the elapse of the preset standby time, the gatingirradiation function 46 a commands the accelerator controller 47 todecelerate the charged particle beam generator 1.

The details of the processing by the gating irradiation function 46 aand the extractable state maintaining function 46 b will be explainedbelow referring to control flow charts of FIGS. 6 and 7.

Control

In order to carry out the irradiation control, the irradiation object 25is set on the couch 24, and the couch 24 with the irradiation object 25is moved to a position specified by the irradiation planning device 41.

FIG. 6 is a control flow chart showing the details of the processing bythe irradiation object monitoring controller 65 and the centralcontroller 46, wherein details of the processing by the acceleratorcontroller 47 and the irradiation controller 48 are shown in simplifiedmanners for convenience of the explanation.

The details of the processing by the irradiation object monitoringcontroller 65 will be explained below.

The irradiation object monitoring controller 65 compares the movementsignal acquired from the irradiation object monitoring device 66 withthe extraction permission area (step S121). The extraction permissionarea may either be specified by the operator before the irradiation orpreviously generated by the irradiation planning device 41.

When the movement signal enters the extraction permission area in thestep S121, the irradiation object monitoring controller 65 sends theextraction permission start signal to the central controller 46 (stepS122). When the movement signal is out of the extraction permissionarea, the irradiation object monitoring controller 65 waits on standbyuntil the judgment in the step S121 becomes affirmative.

Thereafter, the irradiation object monitoring controller 65 compares themovement signal acquired from the irradiation object monitoring device66 with the extraction permission area (step S123). When the movementsignal deviates from the extraction permission area in the step S123,the irradiation object monitoring controller 65 sends an extractionpermission end signal to the central controller 46 (step S124).

Thereafter, this control process is repeated until the completion of theirradiation. The state (period) between the outputting of the extractionpermission start signal and the outputting of the extraction permissionend signal by the irradiation object monitoring controller 65 is set asthe extraction permission state.

Next, the details of the processing by the central controller 46 will beexplained below.

The central controller 46 receives the operator's instruction and sendsan irradiation start signal to the accelerator controller 47 and theirradiation controller 48 (step S101). Further, the central controller46 sends an injection signal to the accelerator controller 47 for theinjection of the beam (step S102) and sends an acceleration signal tothe accelerator controller 47 for the acceleration of the beam (stepS103).

A brief explanation of the processing by the accelerator controller 47corresponding to the steps S101-S103 is inserted here.

The accelerator controller 47 receives the irradiation parameters andgantry angle information from the database 42 via the central controller46. The accelerator controller 47 moves the rotating gantry to a desiredgantry angle according to the received gantry angle information.Further, based on the irradiation parameters, the accelerator controller47 sets the values of the excitation currents for exciting the magnetsof the synchrotron 4 and the beam transport line 2, the value of theradiofrequency wave to be applied by the radiofrequency wave applicationdevice 5, and the value of the radiofrequency wave to be applied to theaccelerator 6, each value corresponding to the ion beam energy Ei foreach slice.

Upon receiving the injection signal, the accelerator controller 47activates the ion source. Ions (e.g., protons (or carbon ions))generated in the ion source are injected into the linear accelerator 3.The linear accelerator 3 accelerates the ions and emits the acceleratedions. The ion beam from the linear accelerator 3 is injected into thesynchrotron 4.

Upon receiving the acceleration signal, the accelerator controller 47accelerates the ion beam (injected into the synchrotron 4 from thelinear accelerator 3) up to the ion beam energy E1 for the slice No. 1by controlling the accelerator 6 and the magnets of the synchrotron 4.In short, the accelerator controller 47 accelerates the ion beam up tointended energy by controlling the charged particle beam generator 1.The acceleration is performed by applying the radiofrequency wave fromthe radiofrequency power supply to the radiofrequency accelerationcavity (i.e., by giving energy to the ion beam circulating in thesynchrotron 4 by using the radiofrequency electric power). Meanwhile,the accelerator controller 47 controls the levels of excitation of themagnets of the beam transport line 2 so that the accelerated ion beamcan be transported to the irradiation nozzle 21. This state is referredto as the extractable state.

The explanation returns to that of the processing by the centralcontroller 46.

Upon recognizing the extractable state, the central controller 46 judgeswhether or not the extraction permission start signal has been receivedfrom the irradiation object monitoring controller 65 (step S104). If theextraction permission start signal has not been received in the stepS104, the central controller 46 waits on standby until the extractionpermission start signal is received. Upon receiving the extractionpermission start signal, the central controller 46 sends an extractionstart signal to the irradiation controller 48 (step S105).

Thereafter, the central controller 46 waits on standby (commandscontinuation of the extraction) until any one of judgments in step S106(whether or not the extraction permission end signal has been received),step S107 (whether or not a dose achievement signal has been received)and step S108 (whether or not a maximum extractable time has elapsed)becomes affirmative.

When the judgment in the step S107 or S108 is affirmative, the centralcontroller 46 sends an extraction stop signal to the irradiationcontroller 48 (step S109) and sends a deceleration signal to theaccelerator controller 47 for the deceleration of the beam (step S110).Incidentally, the dose achievement signal judged in the step S107 is asignal received from the irradiation controller 48. The maximumextractable time judged in the step S108 is the maximum time for whichthe accelerated beam can be maintained in the extractable state. Themaximum extractable time includes the time for which the beam isextracted.

Control that is characteristic of this embodiment will be explainedbelow.

During the continuation of the extraction, the central controller 46judges whether or not the extraction permission end signal has beenreceived from the irradiation object monitoring controller 65 (stepS106). If the extraction permission end signal has been received in thestep S106, the central controller 46 sends the extraction stop signal tothe irradiation controller 48 (step S111).

Thereafter, the central controller 46 waits on standby (commandscontinuation of the stoppage of the extraction) until any one ofjudgments in step S112 (whether or not the extraction permission startsignal has been received again), step S113 (whether or not the presetstandby time has elapsed) and step S114 (whether or not a maximumextractable time has elapsed) becomes affirmative.

If the extraction permission start signal from the irradiation objectmonitoring controller 65 has been received again in the step S112, thecentral controller 46 returns to the step S105 and sends the extractionstart signal again to the irradiation controller 48.

If the preset standby time has elapsed in the step S113 since thereception of the extraction permission end signal, the centralcontroller 46 advances to step S110 and sends the deceleration signal tothe accelerator controller 47 to decelerate the beam. The preset standbytime is the maximum standby time from the reception of the extractionpermission end signal to the start of the deceleration. The presetstandby time may either be set by the operator before the irradiation orpreviously set by the irradiation planning device 41. The preset standbytime may either be changed from irradiation to irradiation or fixed atthe originally determined value.

If the maximum extractable time has elapsed in the step S114, thecentral controller 46 advances to the step S110.

A brief explanation of the processing by the accelerator controller 47corresponding to the step S110 is inserted here.

Upon receiving the deceleration signal, the accelerator controller 47lowers the levels of excitation of the magnets of the synchrotron 4 forthe deceleration and preparation for the injection and thereby sets thesynchrotron 4 in a state in which the beam from the linear accelerator 3can be injected.

The explanation returns to that of the processing by the centralcontroller 46.

The central controller 46 refers to the irradiation controller 48 andjudges whether or not there is a remaining spot (which has not beenirradiated yet) among the spots described in the irradiation parameters(step S115). If there is a remaining spot, the central controller 46returns to the step S102 (injection of the beam) and accelerates thebeam up to the energy for the spot to be irradiated next (step S103). Ifthere is no remaining spot, the central controller 46 sends anirradiation completion signal to the accelerator controller 47 and theirradiation controller 48 (step S116).

FIG. 7 is a control flow chart showing the details of the processing bythe irradiation controller 48, wherein details of the processing by thecentral controller 46 and the accelerator controller 47 are shown insimplified manners for convenience of the explanation.

Upon receiving the irradiation start signal from the central controller46, the irradiation controller 48 starts controlling the irradiationnozzle 21 (step S201). The irradiation is started from slice No. i=1 andspot No. j=1 (step S202).

The irradiation controller 48 excites the scanning magnets 31 and 32with the excitation current values corresponding to the slice No. 1 andthe spot No. 1 calculated by the central controller 46, and thepreparation for the irradiation is thereby completed (step S203).

After completing the irradiation preparation, the irradiation controller48 judges whether or not the extraction start signal from the centralcontroller 46 has been received (step S204). If the extraction startsignal has not been received in the step S204, the irradiationcontroller 48 waits on standby until the extraction start signal isreceived. Upon receiving the extraction start signal, the irradiationcontroller 48 sends an extraction signal to the accelerator controller47 (step S205).

A brief explanation of the processing by the accelerator controller 47corresponding to the step S205 is inserted here.

Upon receiving the extraction signal, the accelerator controller 47starts the extraction of the ion beam from the synchrotron 4 bycontrolling the radiofrequency wave application device 5. Specifically,the accelerator controller 47 connects the aforementioned switch andthereby makes the radiofrequency wave application device 5 apply theradiofrequency wave to the ion beam. The ion beam which has beencirculating in the synchrotron 4 within the stability limit shifts tothe outside of the stability limit and is extracted from the synchrotron4 through the extraction deflector 11. The extracted ion beam passesthrough the beam transport line 2 and enters the irradiation nozzle 21.

Inside the irradiation nozzle 21, the ion beam is scanned by thescanning magnets 31 and 32 and then passes through the beam positionmonitor 33 and the dose monitor 34. Thereafter, the ion beam reaches theirradiation target 37 and stops after giving a prescribed radiation doseto the irradiation target 37.

The explanation returns to that of the processing by the irradiationcontroller 48.

Thereafter, the irradiation controller 48 waits on standby (commandscontinuation of the extraction) until any one of judgments in step S206(whether or not the extraction stop signal has been received) and stepS207 (whether or not the target irradiation amount has reached) becomesaffirmative.

In the step S207, the irradiation controller 48 counts the irradiationamount with a dose counter based on a signal received from the dosemonitor 34. When the value of the dose counter reaches the targetirradiation amount, the irradiation controller 48 judges that theirradiation of the spot j (spot No. j) is completed and sends a stopsignal to the accelerator controller 47 to stop the extraction (stepS208).

Then, the irradiation controller 48 judges whether or not there is aremaining spot in the same slice (step S209). If there is a remainingspot (j<Ni) in the step S209, the irradiation controller 48 incrementsthe value of j by 1 (step S212) and returns to the step S203 toirradiate the next spot. If there is no remaining spot (j=Ni) afterrepeating the spot irradiation, the irradiation controller 48 judgesthat the irradiation of the slice i (slice No. i) is completed and sendsthe dose achievement signal to the central controller 46 (step S210).

Then, the irradiation controller 48 judges whether or not there is aremaining slice (step S211). If there is a remaining slice (i<N) in thestep S211, the irradiation controller 48 increments the value of i by 1(step S214) and returns to the step S203 to irradiate the next slice. Ifthere is no remaining slice (i=N) after repeating the slice irradiation,the irradiation controller 48 judges that the irradiation of all theslices is completed. At this point, the irradiation is completed (stepS215).

In gating irradiation like the one executed in this embodiment, the stopsignal is sent to the accelerator controller 47 to stop the extraction(step S213) when the judgment in the step S206 becomes affirmative, thatis, when the extraction stop signal is received. Thereafter, theirradiation controller 48 returns to the step S204 and waits on standbyuntil the next extraction start signal is received.

A brief explanation of the processing by the accelerator controller 47corresponding to the steps S208 and S213 is inserted here.

Upon receiving the stop signal, the accelerator controller 47 stops theextraction by controlling the radiofrequency wave application device 5.Specifically, the extraction of the ion beam from the synchrotron 4 isstopped by stopping the application of the radiofrequency wave bydisconnecting the switch between the radiofrequency power supply 9 andthe radiofrequency electrodes 8.

Correspondence with Claims

The irradiation object monitoring controller 65 and the steps S122 andS124 executed by the irradiation object monitoring controller 65constitute an extraction permission state setting function of settingthe extraction permission state by outputting the extraction permissionstart signal and the extraction permission end signal in sync with statevariation of the irradiation object 25.

The gating irradiation function 46 a of the central controller 46 andthe steps S104, S105, S106 and S111 executed by the central controller46 constitute an extraction control function of commanding the chargedparticle beam extraction when the charged particle beam generator 1 isin the extractable state and in the extraction permission state, whilecommanding the stoppage of the charged particle beam extraction when thecharged particle beam generator 1 is not in the extraction permissionstate even if the charged particle beam generator 1 is in theextractable state.

The extractable state maintaining function 46 b of the centralcontroller 46 and the step S113 executed by the central controller 46constitute an extractable state maintaining function that operates forthe preset standby time after the reception of the extraction permissionend signal and maintains the extractable state of the charged particlebeam generator 1 even after the end of the extraction permission state.

The gating irradiation function 46 a of the central controller 46 andthe steps S112, S105 and S110 executed by the central controller 46constitute an extraction control function of commanding the chargedparticle beam extraction again when the extraction permission statestarts again during the operation of the extractable state maintainingfunction 46 b (i.e., during the standby time), while commanding thedeceleration of the charged particle beam generator 1 after the end ofthe operation of the extractable state maintaining function 46 b (i.e.,after the elapse of the preset standby time).

Operation

The operation of the charged particle irradiation system according tothis embodiment will be explained below in regard to three differentcases 1-3.

FIG. 8 is a conceptual diagram for explaining the operation of thecharged particle irradiation system, wherein the horizontal axisrepresents the time and the vertical axis represents (from top tobottom) the movement signal, the extraction permission area, theextraction permission state, the accelerator excitation level, theelapse of the standby time, and the beam extraction.

The extraction permission state is set in periods during which themovement signal representing the position of the target 37 is within theextraction permission area. Each extraction permission state is set as astate (period) from the outputting of the extraction permission startsignal to the outputting of the extraction permission end signal.

The accelerator excitation level represents the level of excitation ofthe bending magnets of the synchrotron 4. It is possible to inject thebeam into the synchrotron 4 when the excitation level is low, acceleratethe beam, and thereafter extract the beam from the synchrotron 4 in astate in which the excitation level has become high and constant. Thisstate is referred to as the extractable state. In the extractable state,the extraction of the beam is started in response to the extractionpermission start signal. After the extraction of the beam is stopped inresponse to the extraction permission end signal (in this embodiment,after the preset time has also elapsed), the beam in the synchrotron 4is decelerated by lowering the accelerator excitation level, and thepreparation for the injection of the next beam is started.

(Case 1: Normal Extraction)

When the charged particle beam generator 1 is in the extractable state,the extraction of the beam is started upon the reception of theextraction permission start signal (S101→S102→S103→S122→S104→S105).

In the spot scanning irradiation method, each spot is irradiated withthe beam up to a target dose. After completing the irradiation of a spot(spot irradiation), the next spot irradiation is performed. The spotirradiation is repeated as long as the extraction permission statecontinues (S105→S204→S205→S206→S207→S208→S209→(iteration of S203-S209)).

(Case 2: Gate OFF→Stoppage of Extraction→Deceleration)

The extraction permission end signal is outputted regularly(periodically) due to a regular (periodical) movement signal. The beamextraction is stopped upon the reception of the extraction permissionend signal (S124→S106→S111→S206→S213→(iteration of S204)).

Meanwhile, the extractable state maintaining function 46 b operates uponthe reception of the extraction permission end signal. Thus, the chargedparticle beam generator 1 maintains the extractable state until thepreset standby time elapses. When the preset standby time elapseswithout receiving the extraction permission start signal again duringthe standby time, the extractable state maintaining function 46 bfinishes its operation and the charged particle beam generator 1decelerates the beam (S111→(iteration ofS112→S113→S114)→S112→S113→S110).

(Case 3: Gate OFF→Stoppage of Extraction→Restart of Extraction)

There are also cases where the extraction permission end signal isoutputted irregularly during the irradiation. The beam extraction isstopped upon the reception of the extraction permission end signal(S124→S106→S111→S206→S213→(iteration of S204)).

Meanwhile, the extractable state maintaining function 46 b operates uponthe reception of the extraction permission end signal and the chargedparticle beam generator 1 maintains the extractable state. When theextraction permission start signal is received again during the standbytime, the beam extraction is restarted (S111→(iteration ofS112→S113→S114)→S112→S105→S204→S205).

Effect

The effect of this embodiment will be explained below in contrast withthe conventional technology. The charged particle irradiation systemaccording to the conventional technology does not have the extractablestate maintaining function 46 b (characteristic configuration of thisembodiment).

FIG. 9 is a control flow chart showing the details of the processing bythe central controller 46 according to the conventional technology,wherein steps identical to those in FIG. 6 are assigned the samereference characters as in FIG. 6.

During the continuation of the extraction, the central controller 46judges whether or not the extraction permission end signal has beenreceived from the irradiation object monitoring controller 65 (stepS106). If the extraction permission end signal has been received in thestep S106, the central controller 46 sends the extraction stop signal tothe irradiation controller 48 (step S109) while also sending thedeceleration signal to the accelerator controller 47 to decelerate thebeam (step S110)

FIG. 10 is a conceptual diagram for explaining the operation of thecharged particle irradiation system according to the conventionaltechnology. A case corresponding to the CASE 3 in FIG. 8 will beexplained below.

When the charged particle beam generator 1 is in the extractable state,the extraction of the beam is started upon the reception of theextraction permission start signal (S101→S102→S103→S122→S104→S105). Thespot irradiation is repeated as long as the extraction permission statecontinues (S105→S204→S205→S206→S207→S208→S209→(iteration of S203-S209)).

By the above operation, the spot irradiation in the area a in FIG. 10 iscarried out.

There are also cases where the extraction permission end signal isoutputted irregularly during the irradiation. The beam extraction isstopped upon the reception of the extraction permission end signal(S124→S106→S109→S206→S213→(iteration of S204)).

Meanwhile, upon the reception of the extraction permission end signal,the charged particle beam generator 1 immediately decelerates the beam(S124→S106→S109→S110).

As a result, the spot irradiation in the area b in FIG. 10 cannot becarried out. Since efficient irradiation is impossible as above, thetotal irradiation time tends to be long, and consequently, the treatmenttime is liable to be long in the conventional technology.

Returning to FIG. 8, the operation in the case 3 in this embodimentafter the restart of the beam extraction will be explained below.

When the extraction permission start signal is received again, the beamextraction is restarted and the spot irradiation is repeated(S112→S105→S204→S205-S209→(iteration of S203-S209)).

The extraction permission end signal is outputted regularly(periodically) due to a regular (periodical) movement signal. The beamextraction is stopped upon the reception of the extraction permissionend signal (S124→S106→S111→S206→S213→(iteration of S204)).

As a result, the spot irradiation in the area b′ in FIG. 8 is carriedout. Owing to the efficient irradiation, the irradiation time and thetreatment time can be shortened.

Modifications

The present invention is not to be restricted to the above embodiment; avariety of modifications are possible.

1. Various modifications are possible in regard to the starting point ofthe operation of the extractable state maintaining function 46 b. Whilethe extractable state maintaining function 46 b in the above embodimentstarts waiting on standby for the preset standby time upon the receptionof the extraction permission end signal outputted from the irradiationobject monitoring controller 65 in the step S124, the extractable statemaintaining function 46 b may also be configured to start waiting onstandby for the preset standby time upon the transmission of theextraction stop signal to the irradiation controller 48 in the stepS111, for example.

2. Various modifications are possible in regard to the setting of theextraction permission state. While the irradiation object monitoringcontroller 65 in the above embodiment sets the extraction permissionstate as the state (period) from the outputting of the extractionpermission start signal to the outputting of the extraction permissionend signal, the extraction permission signal may also be outputtedcontinuously and the extraction permission state may be set as a state(period) from the start of the outputting of the extraction permissionsignal to the end of the outputting of the extraction permission signal.

3. While the above embodiment has been explained assuming the use of thespot scanning irradiation method as the irradiation method, theembodiment is applicable also to the double scattering irradiationmethod (broadening the distribution of the beam by using a scatterer)and the wobbler irradiation method (scanning the beam (broadened with ascatterer) in a circular pattern).

Second Embodiment

FIG. 11 is a control flow chart showing the details of the processing bythe central controller 46 according to a second embodiment of thepresent invention, wherein steps identical to those in FIG. 6 areassigned the same reference characters as in FIG. 6.

The extractable state maintaining function 46 b in the first embodimentoperates just for the preset standby time after the reception of theextraction permission end signal (S113 in FIG. 6). The extractable statemaintaining function 46 b in the second embodiment may be configured tooperate after the reception of the extraction permission end signaluntil a deceleration start command signal is received, that is, whilethe movement signal after deviating from the extraction permission areadoes not exceed a deceleration start command value (S113A in FIG. 11).

After sending the extraction permission end signal to the centralcontroller 46 in the step S124, the irradiation object monitoringcontroller 65 judges whether or not the movement signal has exceeded thedeceleration start command value which has been set outside theextraction permission area (step S125). When the movement signal exceedsthe deceleration start command value, the irradiation object monitoringcontroller 65 sends the deceleration start command signal to the centralcontroller 46 (step S126).

FIG. 12 is a conceptual diagram for explaining the operation of thecharged particle irradiation system according to the second embodiment.

The extraction permission state is set in periods during which themovement signal representing the position of the target 37 is within theextraction permission area. The charged particle beam generator 1accelerates the beam and shifts to the extractable state. The beamextraction is started in response to the extraction permission startsignal (case 1).

The beam extraction is stopped in response to the extraction permissionend signal. Meanwhile, the extractable state maintaining function 46 boperates and the charged particle beam generator 1 maintains theextractable state (standby).

When the movement signal representing the position of the target 37exceeds the deceleration start command value, the deceleration startcommand signal is outputted.

When the deceleration start command signal is received without receivingthe extraction permission start signal again during the standby time,the extractable state maintaining function 46 b finishes its operationand the charged particle beam generator 1 decelerates the beam (case 2).

The beam extraction is stopped during the irradiation due to thereception of the irregular extraction permission end signal. Meanwhile,upon the reception of the extraction permission end signal, theextractable state maintaining function 46 b operates and the chargedparticle beam generator 1 maintains the extractable state. When theextraction permission start signal is received again during the standbytime, the beam extraction is restarted (case 3).

The operation of the charged particle irradiation system in the secondembodiment is substantially equivalent to that in the first embodimentand effects similar to those of the first embodiment are achieved.

Third Embodiment

FIG. 13 is a control flow chart showing the details of the processing bythe irradiation controller 48 according to a third embodiment of thepresent invention, wherein steps identical to those in FIG. 7 areassigned the same reference characters as in FIG. 7.

While the extraction is stopped during the spot irradiation in the firstembodiment upon the reception of the extraction stop signal (S206→S213),it is also possible to shift to the standby state after completing thespot irradiation. Thus, the steps S206 and S213 are unnecessary in thisembodiment.

In cases where the irradiation time for each spot is short and themovement of the target during the time is negligible, the control can besimplified compared to the first embodiment by not stopping theirradiation in the middle of the spot irradiation.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 charged particle beam generator-   2 beam transport line-   3 linear accelerator-   4 synchrotron-   5 radiofrequency wave application device-   6 accelerator-   7 control system-   8 radiofrequency electrode-   9 radiofrequency power supply-   11 extraction deflector-   12 beam path-   14, 15, 16 bending magnet-   17 treatment room-   21 irradiation nozzle-   24 couch-   25 irradiation object-   31, 32 scanning magnet-   33 beam position monitor-   34 dose monitor-   37 irradiation target-   40 X-ray CT device-   41 irradiation planning device-   42 database-   46 central controller-   46 a gating irradiation function-   46 b extractable state maintaining function-   47 accelerator controller-   48 irradiation controller-   65 irradiation object monitoring controller-   66 irradiation object monitoring device

The invention claimed is:
 1. A charged particle irradiation system comprising: a charged particle beam generator that generates a charged particle beam; and a control system that controls the charged particle beam generator including extraction of the charged particle beam in accordance with an extraction permission state that is associated with a state variation of an irradiation object, and after an extraction of the charged particle beam is stopped in association with the state variation of the irradiation object which is irradiated with the charged particle beam, the charged particle beam generator is controlled to maintain an extractable state which can start the irradiation of the irradiation object based on the extraction permission state in association with the state of variation of the irradiation object.
 2. The charged particle irradiation system according to claim 1, wherein a period from an end of a change of an energy level of the charged particle beam to a start of a next change of the energy level of the charged particle beam or a next deceleration of the charged particle beam is variable.
 3. The charged particle irradiation system according to claim 1, wherein a period from an end of an acceleration of the charged particle beam to a start of a next deceleration of the charged particle beam is variable.
 4. The charged particle irradiation system according to claim 1, wherein the charged particle beam generator is controlled to maintain the extractable state for a preset standby time which starts the irradiation of the irradiation object based on the extraction permission state in association with the state variation of the irradiation object.
 5. The charged particle irradiation system according to claim 4, wherein the charged particle beam generator starts to be controlled to maintain the extractable state which starts the irradiation of the irradiation object based on the extraction permission state in association with the state variation of the irradiation objected based on a signal that commands termination of the extraction permission state.
 6. The charged particle irradiation system according to claim 4, wherein the charged particle beam generator starts to be controlled to maintain the extractable state which starts the irradiation of the irradiation object based on the extraction permission state in association with the state variation of the irradiation object based on a signal that commands the stoppage of the charged particle beam extraction.
 7. The charged particle irradiation system according to claim 1, wherein the charged particle beam generator is controlled to maintain the extractable state which starts the irradiation of the irradiation object based on the extraction permission state in association with the state variation of the irradiation object only while the state variation of the irradiation object is within a preset range.
 8. The charged particle irradiation system according to claim 1, wherein the control system controls the charged particle beam generator to stop the extraction of the charged particle beam after reception of a signal commanding termination of the extraction permission state and after the irradiation of the irradiation object with a prescribed dose.
 9. A charged particle irradiation system comprising: a charged particle beam generator that repeats injection of charged particles, acceleration of the charged particles to an extractable state after finishing the acceleration, and deceleration of the charged particles; and a control system that controls extraction of a charged particle beam of the charged particles in accordance with an extraction permission state that is associated with a state variation of an irradiation object and that maintains the extractable state of the charged particles after extraction is stopped based on the extraction permission state in association with the state variation of the irradiation object.
 10. The charged particle irradiation system according to claim 9, wherein a period of the extractable state of the charged particles is variable.
 11. The charged particle irradiation system according to claim 9, wherein the control system maintains the extractable state of the charged particles for a preset standby time.
 12. The charged particle irradiation system according to claim 11, wherein the control system starts to maintain the extractable state of the charged particles based on a signal that commands termination of the extraction permission state.
 13. The charged particle irradiation system according to claim 11, wherein the control system starts to maintain the extractable state of the charged particles based on a signal that commands the stoppage of the charged particle beam extraction.
 14. The charged particle irradiation system according to claim 9, wherein the control system maintains the extractable state only while the state variation of the irradiation object is within a preset range.
 15. The charged particle irradiation system according to claim 9, wherein the control system commands the stoppage of the charged particle beam extraction after reception of a signal commanding termination of the extraction permission state and after irradiation with a prescribed dose.
 16. A charged particle irradiation method comprising: generating a charged particle beam; controlling extraction of the charged particle beam in accordance with an extraction permission state that is associated with a state variation of an irradiation object; when extraction of the charged particle beam is stopped in association with the state variation of the irradiation object which is irradiated with the charged particle beam, controlling the generation of the charged particle beam to maintain an extractable state which can start the irradiation of the irradiation object beam based on the extraction permission state in association with the state of variation of the irradiation object.
 17. A charged particle irradiation system comprising: a charged particle beam generator that generates a charged particle beam; and a control system that controls the charged particle beam generator including extraction of the charged particle beam in accordance with an extraction permission state that is associated with a state variation of an irradiation object, and after an extraction of the charged particle beam is stopped in association with the state variation of the irradiation object which is irradiated with the charged particle beam, the charged particle beam generator is controlled so that the charged particle beam is kept ready for extraction based on the extraction permission state in association with the state of variation of the irradiation object. 